So i went ahead and got myself an airport extreme as i need a new router. I have an external 1TB drive plugged in, and am able to access while on the network with no problems via mac, iphone and ipad.

However i am having some difficulty in seeing a way to connect outside the network via iOS. At the moment (temporary setup, not my chocie) i have the following setup, which seems to give me a hard time connecting otuside via any device.